In 2011, 2.71 million Muslims lived in England and Wales, compared with 1.55 million in 2001. [Muslim population in England and Wales nearly doubles in 10 years by Aisha Gani; The Guardian, Feb. 11th 2015. ]Using linear inter-/extrapolation, that gives 2.01m for 2005 and 3.17m for today.
So here is Britain's policy response towards domestic Muslim terrorism: Permit the Muslim population to increase by over 100,000 a year for a decade.
If despair is truly a sin, then contemplating the immigration policies of Western nations offers an exceptionally challenging spiritual test.